1. Field of the Invention
The present invention relates to a decoding apparatus and data reproduction apparatus for decoding an RF signal read from a digital audio disk called a CD (compact disk) or MD (Mini Disc) or other information storage medium storing information using a RLL (run length limited) code and outputting channel bit data and a method of the same.
2. Description of the Related Art
When transmitting data or, for example, storing data on a magnetic disk, optical disk, magneto optic disk, or other storage medium, the data is modulated so as to make it suitable for the transmission or storage.
A block code is known as one of such modulating codes.
A block code divides a data series into blocks of units comprised of mxc3x97i bits and convert the data words into codes comprised of nxc3x97i bits in accordance with an appropriate coding rule.
This block code becomes a fixed length code when i=1. When a plurality of i""s can be selected, that is, when i is 2 or more and converting by a maximum i of imax=r, it becomes a variable length code.
The block coded code is expressed as a variable length code (d, k;m, n;r).
Here, i indicates a constraint length and r indicates a maximum constraint length. d and k are a minimum consecutive number of xe2x80x9c0""sxe2x80x9d and a maximum consecutive number of xe2x80x9c0""sxe2x80x9d inserted between consecutive xe2x80x9c1""sxe2x80x9d in a code series.
A modulation format of a digital audio disk will be explained as a specific example below.
In a digital audio disk, for example, in a disk of a CD format, a modulation system called EFM (Eight to Fourteen Modulation) is adopted.
Data recorded on a CD is comprised of 16 bits of digital data sampled at 44.1 kHz then divided into two, that is, 8 bits of the upper side and 8 bits of the lower side, subjected to interleaving, and given parity bits along with a C1 and C2 series.
8-bit data words are converted in pattern (EFM modulation) to predetermined 14-bit code words (channel bits), then 3-bit connection bits are added between the data in order to reduce the direct current component after the EFM modulation, and the result is written on the disk by NRZI.
In order to satisfy the conditions that the minimum consecutive number of xe2x80x9c0""sxe2x80x9d inserted between consecutive xe2x80x9c1""sxe2x80x9d in a code series be 2 and the maximum consecutive number of xe2x80x9c0""sxe2x80x9d be 10, 8 bits are converted to 16 bits and connection bits are added.
Accordingly, the parameter (d, k;m, n;r) of this modulation system is (2, 10;8, 17;1).
When the bit interval of a channel bit series (storage waveform series) is T, the minimum inversion interval Tmin becomes 3(=2+1)T. Further, the maximum inversion interval Tmax becomes 11(=10+1)T.
Namely, the data to be converted from 8 bits to 16 bits and given connection bits is finally reduced to a length from 3T to 11T (1/T=4.3218 MHz, one time).
When demodulating this EFM signal, a clock (hereinafter referred to as a playback clock) is generated based on a binary pulse series signal obtained by waveform shaping of an RF signal read from the disk and the playback clock is used for demodulating. When generating the playback clock, a PLL (Phase Locked Loop) circuit is generally used.
The frequency of the playback clock PCK is 4.3218 MHz. This 4.3218 MHz is the channel clock frequency when modulating an EFM signal by PWM by the CD format. The EFM signal is modulated by PWM in one cycle steps from the 3rd cycle to the 11th cycle.
The binary signal obtained by conversion of the RF signal read from the disk to a binary format by waveform shaping is a signal which changes in nT, where T is a cycle of the channel clock (n is an integer from 3 to 11).
In a CD system, however, when an input RF signal is converted to a binary format and demodulated by EFM, the 3T of the EFM signal is sometimes detected as 1T or 2T due to damage or deviation of the comparison level.
In a decoding apparatus of a CD system of the related art, this is not corrected in any way. EFM signals outside 3T to 11T are dealt with as errors as inherently impossible signals and are corrected by an internal error correction circuit.
However, there are limits to the error correction capability of an error correction circuit, so when 1T and 2T are randomly included more than a certain amount, they cannot be corrected by the error correction circuit in the above decoding apparatus of the CD system of the related art and the playability deteriorates.
The present invention was made in consideration with such a circumstance and has as an object thereof to provide a decoding apparatus and data reproduction apparatus enabling correction of inherently impossible 1T and 2T, enabling reduction of the processing of the error correction circuit, and enabling improvement of the playability and a decoding method for the same.
To achieve the above object, the present invention provides a decoding apparatus for decoding a code which has a consecutive length, the length being a length of symbol arranged consecutively between identical other symbols of a code series formed by two symbols, defined as a predetermined defined length and which has a minimum inversion interval of 3T, where T is a bit interval of a channel bit series, comprising a detecting means for detecting from the code series a pattern of T""s which has a minimum inversion interval of smaller than 3T and inherently does not exist in normal cases and a correcting means for correcting any pattern of T""s which inherently does not exist detected by the detecting means to signals of a normal format of 3T or more.
Further, the present invention provides a data reproduction apparatus for reproducing code data which has a consecutive length, the length being a length of symbol arranged consecutively between identical other symbols of a code series formed by two symbols, defined as a predetermined defined length and which has a minimum inversion interval of 3T, where T is a bit interval of a channel bit series (storage waveform series) stored on a predetermined storage medium, comprising a means for reproducing an RF signal from the storage medium; a detecting means for detecting from the reproduced RF signal a pattern of T""s which has a minimum inversion interval of smaller than 3T and inherently does not exist in normal cases; a correcting means for correcting any pattern of T""s which inherently does not exist detected by the detecting means to signals of a normal format of 3T or more; and an error correction circuit for correcting error in the signals corrected by the correcting means.
Further, in the present invention, the detecting means detects a pattern of consecutive T""s including 1T and the correcting means removes a 1T portion to correct any detected pattern of consecutive T""s including 1T to signals of a normal format of 3T or more.
Alternatively, in the present invention, the detecting means detects a pattern of consecutive T""s including 1T and the correcting means corrects an 1T portion of any detected pattern of consecutive T""s including 1T to 3T.
Alternatively, in the present invention, the detecting means detects a consecutive pattern including 1T and the correcting means corrects any detected consecutive pattern including 1T to signals of any format of 3T or more.
Alternatively, in the present invention, the detecting means detects a pattern of consecutive T""s including 1T and 2T and the correcting means corrects any detected pattern of consecutive T""s including 1T and 2T to signals of any format of 3T or more.
Alternatively, in the present invention, the detecting means detects a pattern of consecutive T""s including 2T and the correcting means removes the 2T portion to correct any detected pattern of consecutive T""s including 2T to signals of a normal format of 3T or more.
Alternatively, in the present invention, the detecting means detects a pattern of consecutive T""s including 2T and the correcting means corrects a 2T portion of any detected pattern of consecutive T""s including 2T to 3T.
Alternatively, in the present invention, the detecting means detects a consecutive pattern including 2T and the correcting means corrects any detected consecutive pattern including 2T to signals of any format of 3T.
Alternatively, in the present invention, the correcting means compares the lengths of T""s in front of and in back of the 2T portion of any detected 2T portion and corrects the 2T to the longer side.
Alternatively, in the present invention, the correcting means compares phase errors of edges of binary signals of 2T, determines in accordance with the comparison results in which direction in front of or in back of the 2T portion to correct the portion, and corrects the 2T to 3T in the determined direction.
Alternatively, in the present invention, the correcting means coercively extends any detected 2T portion by 1T in front of or in back of it to correct it to 3T.
Alternatively, in the present invention, the correcting means coercively extends every detected 2T by 1T alternately in the direction in front of and in back of it.
Alternatively, in the present invention, the correcting means coercively extends any detected 1T by 1T in front of and in back of it to correct it to 3T.
Alternatively, in the present invention, the correcting means comprises a first correction circuit for removing any detected 1T to correct the 1T portion to signals of a normal format of 3T or more; a second correction circuit for correcting any 2T portion detected from output signals of the first correction circuit to 3T; a third correction circuit for comparing phase errors of edges of binary signals of any detected 2T, determining in accordance with the comparison results in which direction in front of or in back of the 2T portion to correct it, and correcting the 2T to 3T in the determined direction; and a fourth correction circuit for correcting any 1T portion detected from output signals of the third correction circuit to 3T.
Alternatively, in the present invention, there is further comprised a means enabling switching of connection of positions of signal lines of the third correction circuit and the fourth correction circuit between an output of the second correction circuit and an output of the correcting means.
Further, the present invention provides a decoding method for decoding a code which has a consecutive length, the length being a length of symbol arranged consecutively between identical other symbols of a code series formed by two symbols, defined as a predetermined defined length and which has a minimum inversion interval of 3T, where T is a bit interval of a channel bit series, comprising detecting from the code series a pattern of T""s which has a minimum inversion interval of smaller than 3T and inherently does not exist in normal cases and correcting any detected pattern of T""s, which inherently does not exist to signals of a normal format of 3T or more.
According to the present invention, at least one of 1T or 2T, which are patterns of T""s where the minimum inversion interval is less than 3T and which inherently does not exist in normal cases, is detected in the detecting means from a code series.
Further, when an inherently impossible pattern of T""s is detected by the detecting means, the pattern is corrected in the correcting means to signals of a normal format of 3T or more.
Further, according to the present invention, an RF signal is reproduced from a storage medium.
Then, at least one of 1T or 2T, which are patterns of T where the minimum inversion interval is less than 3T and which inherently does not exist in normal cases, is detected by the detecting means from the reproduced RE signal.
Further, when an inherently impossible pattern of T""s is detected by the detecting means, the pattern is corrected in the correcting means to signals of a normal format of 3T or more.
The corrected signal is input to the error correction circuit where the error is corrected.
By correcting the generated 1T and 2T signals in the above way, signals which have been regarded as errors before can be restored. Therefore, the signals to be corrected in the error correction circuit are corrected to a format from 3T to 11T, so the result is that the error rate is improved and the playability is improved.
Furthermore, 1T and 2T signals generated as a result of the amplitude level of the RF signal declining and the RF signal not correctly being input due to fine scratches on the disk surface or signals not precisely converted to a binary format can be removed.